1. Field of the Invention
The present invention relates to an imaging apparatus configured to pick up an image of an object.
2. Description of the Related Art
In shooting a still image with an imaging apparatus such as a digital camera and a video camera, in order to confirm an object to be shot in a still image, image data serially read from an image sensor such as a complementary metal-oxide semiconductor (CMOS) image sensor, is displayed by an image display unit as a serial image.
In this state, a photographer half presses a shutter button and then an operation such as focusing is performed. After that, the photographer fully presses the shutter button to photograph a still image (see, for example, Japanese Patent Application Laid-Open No. 2005-223588, Japanese Patent Application Laid-Open No. 09-163218, and Japanese Patent Application Laid-Open No. 2000-115642).
An image sensor such as a CMOS image sensor includes an output amplifier that amplifies and outputs signals from a plurality of photoelectric conversion units. Until a still image shooting is performed, image data serially read from the image sensor is displayed by an image display unit as a serial image, and accordingly, power is continuously supplied to the output amplifier for that period of time. Thus, a temperature of the image sensor keeps rising. In the image sensor, an effect of dark current increases as the length of a time period starting with resetting of photoelectric conversion units and ending at reading of signals from the image sensor becomes longer. Especially in a state where the temperature of the image sensor is high, an effect of dark current is significant.
That is, when the temperature of an image sensor is high before an operation for shooting a still image is started, a still image obtained by performing a still image shooting operation is affected by dark current.
In shooting a still image, a very large number of signals are read from an image sensor, and accordingly, a time period starting with resetting of photoelectric conversion units and ending at reading of signals from the image sensor becomes long. In addition, when a long time exposure (shooting whose accumulation time is long) is performed, a time period starting with resetting of photoelectric conversion units and ending at reading of signals from an image sensor becomes very long, and accordingly, dark current significantly affects an image.